The proposed research is part of a long-term project to purify and characterize the structural proteins of feline virus (FeLV) and then study their synthesis in vivo and in vitro. The purification and characterization is already partially completed and will be continued. Proteins are separated by gel filtration on 6% and 8% agarose in the presence of 6 M guanidine-HCl and reducing agent. Further purification and analysis will be done by isoelectric focusing, gel electrophoresis, and other methods of chromatography. Molecular weights will be determined by the gel filtration procedure and by SDS-polyacrylamide gel electrophoresis. Purified proteins will be used to determine tryptic peptide maps, amino acid analysis and to provide monospecific antisera. Whenever possible iodination will be used to facilitate analysis of minority species of protein and to prepare marker proteins. Synthesis of viral proteins will be studied to determine the size and nature of the viral mRNA and its translation products. Initial studies will be done in vitro using purified 70 viral RNA and its S35 subunits in a Novikoff hepatoma cell-free system. The in vitro product will be analyzed in comparison with the purified viral proteins using the same analytical methods and monospecific antisera. Similar studies will be extended to viral polypeptides synthesized in vivo in chronically infected feline thymus tumor cells. Pulse-chase experiments will be included to follow possible post-translational cleavage or other processing as the proteins leave the polyribosome and become part of the virion. To facilitate the study of nascent viral polypeptides and viral mRNA, virus specific polyribosomes will be separated from the cellular structures by immunoabsorbent procedures using monospecific antisera. Viral mRNA will be identified by a molecular probe of in vitro synthesize complementary DNA. Viral RNA obtained by these methods will be analyzed for its size, Poly A content, and ability to act as template in the in vitro system assuming sufficient material can be isolated.